Accurate measurement and control of sample temperature have long been a problem in nuclear magnetic resonance (NMR) spectroscopy. When high-power heteronuclear decoupling is used, interaction between the radiofrequency electric field and the electric dipole moments of molecules and ions in the sample causes the sample to be heated and usually increases the uncertainty of temperature measurement. In cases where the ionic conductivity of the sample is low, heat generation due to absorption of RF energy is relatively small, and errors in temperature measurements may be made correspondingly small. Heating effects become large for aqueous solutions of high ionic strength and the temperature at various locations in the active volume of the sample may be far from uniform.
Heating effects are of special concern in dynamic NMR studies of rate processes and chemical equilibria. Dipolar relaxation rates and NOEs in systems where molecular reorientation is cooperative may also be sensitive to temperature dispersion arising from RF heating. Determinations of rotational correlation times and conformer distribution in biopolymer or liquid-crystalline lipid systems thus require that temperature be highly uniform and time-invariant throughout the active volume and that it be known accurately.
The present invention is directed to an improved insert for use in a sample tube for reducing the effects of radio frequency heating on the sample temperature.